[order] Ciconiiformes | [family] Ardeidae | [latin] Ixobrychus exilis | [UK] Least Bittern | [FR] Petit Blongios | [DE] Amerikanische Zwergdommel | [ES] Avetorillo Panamericano | [IT] Tarabusino minore americano | [NL] Amerikaans Woudaapje

Amerikaans Woudaapje determination

copyright: J. del Hoyo

The Least Bittern is the smallest of all the herons. Adult male has glossy greenish-black back. Wing coverts are pale greyish-brown, tipped with yellowish-brown. Inner secondaries are broadly edges with pale chestnut. Secondary coverts and edge of the wing at the flexure are pale chestnut. Tail is greenish-black. Buff wing coverts are visible in flight and at rest. Flight feathers are blackish. Underparts are pale buff. It has black tufts on chest sides, usually concealed. Belly and undertail coverts are whitish. On the head, crown is greenish-black. Sides of the head and hind neck are brownish-red or light chestnut. Chin and throat are whitish. Foreneck is pale buff, with fairly faint brown streaks.
Bill is longer than the head, about 4 cm. It is orange with dusky culmen. Lores are yellow-green. Eyes are pale yellow. Legs are greenish-yellow. Feet are yellow. Female resembles male, but crown and mantle are dark brown, and we can see conspicuous dark streaking on underparts, and duller colours on wings. Juvenile resembles female with paler and browner crown, and with more prominent streaking on back and crest. Bill is dusky pink to yellowish, with dark tip. We can also find the Cory' Least Bittern, a very rare dark morph, with dark brown colours instead brownish-red on neck, sides and front.

Least Bittern lives in large marshes with dense vegetation, freshwater marshes, lakes and pools with dense fringing vegetation, but also in mangroves and brackish marshes.

Least Bittern can feed in deeper water than other herons, due to its habits of straddling reeds. It stalks preys along the reeds, sometimes in deep water, or it climbs on the reed stems, and then it strikes downwards into the water with its bill. It feeds in small pools among emergent vegetation, walking slowly at the edges of the water. It stands and waits, with legs spread apart, head and neck lowered out over the pool, and bill almost touching the water. After a capture, Least Bittern retreats back into vegetation, and moves to another pool. Least Bittern is a shy bird. It lives an overwater life, hidden in the dense vegetation of marsh. When an intruder approaches, it runs away instead of takes off. When flushed, it moves low over the top of the emergent vegetation. It flies short distances before dropping back into vegetation. When Least Bittern is walking or running through the vegetation, it uses plant stalks as steeping-stones. With its legs spread apart, it grasps one or several stalks with each foot, and steps along. If alarmed or threatened, Least Bittern may freeze in place with bill pointed upright. With its brownish plumage, in this posture, it is very well camouflaged. It also may sway from side to side, following the reeds in the wind. During courtship displays, male and female utter some sounds, one responding to the other. They are monogamous.

Least Bittern feeds on small fish and aquatic invertebrates, but also on reptiles, amphibians and insects, which captures with quick jabs of its bill. It also may feed on eggs and chicks of other marsh species.

This species has a large range, with an estimated global Extent of Occurrence of 6,200,000 kmē. It has a large global population estimated to be 130,000 individuals (Wetlands International 2002). Global population trends have not been quantified, but the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e. declining more than 30% in ten years or three generations). For these reasons, the species is evaluated as Least Concern. [conservation status from birdlife.org]

Least Bittern nests sometimes in loose colonies. Nest is a frail platform above the water, built on bent-down, dead stalks of emergent vegetation. Nest is built mainly by the male, and made with dead and fresh plant stems, with a canopy made with tall marsh plants pulled over the platform. Female lays 2 to 5 bluish-white eggs, sparsely flecked with brown; incubation lasts about 19 to 20 days, shared by both parents. Particular ceremonial has been observed when adults take their turns. The bird on the nest erects its crown feathers, while calling "gra-a-a". The other bird also fluffs crown and body feathers. When both birds are on the nest, they open their mandibles and shake their bills from side to side, with a rattling sound. This ceremonial occurs in nest relief, but also when a bird returns to the nest. Young are fed by both adults. They are covered with rusty-brown down on back, whitish below. They fledge at about 25 days after hatching. This species may produce two broods per season.

Nominate exilis performs widespread post-breeding dispersal, and also long distance migration from N of range, leaving in Sept-Nov and returning in Feb-Apr, or in May in extreme N; winters from S USA through C America and Caribbean to N South America; birds from W USA migrate through W Mexico as far as Costa Rica. Migration apparently takes place by night. Straggler to N of breeding range in British Columbia and Newfoundland; accidental to Iceland and Azores. Other races seem to be sedentary, though can apparently perform some movements due to failure of seasonal rains.